Method for producing a plastics product and device for carrying out the method and also closure product or adhesion product produced by the method and the device

ABSTRACT

A method for producing a plastics product consisting of a support ( 30 ) having protruding stem parts ( 36 ) which have at their free end a head part ( 38 ) having a wider diameter compared with the respective stem part ( 36 ), wherein the stem parts and the head parts are formed in cavities ( 16 ) of a moulding screen ( 12 ) that are formed, on their sides facing away from the support ( 30 ), in a shaping zone of the moulding screen ( 12 ), is characterized in that the shaping zone is sealed off from the environment by means of a counter-surface ( 20 ) such that a predefinable amount of air enclosed in the shaping zone exerts a counter-pressure on the plastics material introduced into the respective cavity ( 16 ) of the shaping zone in order to support the shaping process.

The invention relates to a method for producing a plastic productconsisting of a support having protruding stem parts, which have attheir free end a head part having a wider diameter as compared to therespective stem part, wherein the stem and the head parts are formed incavities of a molding screen, which cavities are formed on the sidethereof facing away from the support in a shaping zone of the moldingscreen. The invention further relates to a device for carrying out themethod as well as a closure or adhesion product, which is producedaccording to this method or using this device.

A method for the production of a closure product is known from DE 196 46318 A1, which method has a plurality of hooking means integrally formedhaving a support in the form of stem parts having thickened sections, inwhich stem parts a thermoplastic is introduced, in plastic or fluidform, into the gap between a compression roller and a molding roller,wherein the molding roller is provided with hollow spaces that are opento the inside and the outside, and wherein both rollers are driven inopposite directions of rotation, so that the support is formed in thegap between the rollers. The known method, which is also genericallyassigned to the so-called chili-roll method, is characterized in thatthe molding roller has a screen, the cavities of which are produced byetching or by means of a laser, wherein finished mushroom-shaped hookingmeans arise simply in that the thermoplastic in the open hollow spacesof the screen of the molding roller is at least partially hardened. Inthe prior art, a low-cost manufacturing process for producing closureparts made of thermoplastic is herewith created in addition to theassociated production device, wherein such mushroom-shaped hooking meanscan be loosely meshed with looped parts and/or otherwise correspondinghooking means of an additional closure part in order to form a closurethat can be repeatedly opened and closed. Such closure systems are alsoknown throughout the world under the brand name Kletten® or Kletten®hook and loop fasteners, at least in the professional world.

A method for producing adhesion elements on a support by means of usingat least one plastic material is now known from DE 10 2004 012 067 A 1,which material is introduced into at least one molding element. Adhesiveelements are created by means of the known method having ends on thestems that widen as head parts, the adhesion of which is primarilyobtained by van der Waals forces. In the case of the known method, therespective plastic material used is preferably thixotropic and has aviscosity, measured using a rotation viscometer, of 7,000 to 15,000mPas. In addition, a drum or band-shaped screen is then used as arespective molding element, wherein in this case however, this elementis provided with at least 10,000, preferably with 16,000 or more moldingcavities per cm².

Van der Waals forces are so-called intermolecular forces, which occur asweak binding forces between inert atoms and saturated molecules. Whileonly the so-called dispersion forces come into play in the interactionbetween atoms, the interactions of induced or potentially permanentlyexisting dipole moments (orientation effect) in molecules act asadditional forces of attraction. It should be noted that although someauthors treat the term “van der Waals forces” as a synonymous withintermolecular forces, the majority understand “van der Waals forces” toalso refer to those very far-reaching forces of attraction betweenneutral molecules.

Using the known method, as well as device and product solution, adhesionsystems may be implemented, in which the adhesion product can be fixedto any surfaces. In addition to fastening options of this sort, newapplications in medical technology have also been developed in therecent past, for example for wound and burn care.

In the case of these known solutions, the molding of the plasticmaterial in the molding cavities of the molding screen is done slowly,in order to obtain a configuration of the regular, mushroom-shapedclosure head as a respective head part, the shape of which is as stableas possible, with the proviso that after adequate curing time, thisclosure head can be well formed by the screen in order to make theclosure product or the adhesion product.

Accordingly, the object of the present invention is to provide a methodand device, which not only allows the uniform molding of the head andstem parts by the molding screen, but also allows significantly fastermolding, so that significantly faster production speeds are thereby madepossible, which in turn, helps to lower production costs. A furtherobject of the invention is to obtain an advantageous embodiment of theclosure or adhesion product by means of the method according to theinvention and device.

Such an object is achieved with the method according to theconfiguration of features of claim 1 in its entirety.

Since, pursuant to the method according to the invention, the shapingzone is sealed off from the environment by means of a counter-face insuch a way that a predeterminable quantity of air enclosed in theshaping zone exerts a counter-pressure on the plastic materialintroduced into the respective cavity of the shaping zone in order tosupport the shaping process, the penetration of the plastic melt intothe respective molding cavity is made more difficult by the enclosedquantity of air so that, in addition to a compression of the melt, thereis also an improved orientation of the plastic material within theshaping zone. The result is that, in particular, the head parts that areto be formed are oriented along the molding walls of the respectivecavity within the shaping zone and also harden more rapidly, so that thedemolding process can proceed more quickly, which helps to reduce theproduction costs for the closure or adhesion product being produced.

As a result of the quantity of air enclosed in the respective cavitybetween the aforementioned counter-face and the shaping zone, into whichplastic melt has been introduced, additional molding pressure is appliedto the upper side of the respective head part by means of the air thusenclosed, so that an increased contact pressure arises between theperipheral edges of the head part and the adjacently disposedcircumferential molding wall of the cavity. As a result of thisincreased contact pressure, in addition to the directional orientationfor the respective closure or adhesive head part, which leads toimproved strength properties, the curing process is accelerated, whichdetermines faster molding times.

In addition, the above mentioned object is also achieved by a device forcarrying out the aforementioned method, wherein the above mentionedshaping zone of the molding screen is sealed off from the environment bymeans of the counter-face in such a way that a predeterminable quantityof air enclosed in the shaping zone exerts a counter-pressure on theplastic material introduced into the respective cavity of the shapingzone in order to support the shaping process.

The closure or adhesion product that is thus obtained, which likewiseachieves the object according to the invention, is specificallycharacterized in that the height of the product between the underside ofthe support and the upper side of the support is minimized in such away, preferably equaling 40 to 120 μm, particularly preferably 70 to 110μm, that the product has elastic properties at least in partial regions,in particular in the longitudinal direction of the support. As a whole,when compared to the prior art, it is possible to obtain closure oradhesion products by means of the method according to the invention anddevice, which in addition to increased peel strength values, includingin terms of material strength, can be made significantly thinner, whichresults in softer and more flexible closure or adhesion products. Suchproducts, which make a softer and more flexible impression, can then beeasily processed within hygiene products such as baby diapers and thelike, where it is essential that the product be tolerated by, and workwell with, the skin.

Additional advantageous embodiments of the solution according to theinvention are the subject of the dependent claims.

In the following, the method according to the invention is explained ingreater detail based on two devices for carrying out the method inaddition to the closure or adhesion product thus obtained. The figuresare schematic and not to scale:

FIG. 1 a longitudinal section of a first embodiment of the deviceaccording to the invention;

FIG. 2 an enlarged longitudinal section of a detail indicated in FIG. 1as X;

FIG. 3 a further embodiment of a manufacturing device according to theinvention comparable to FIG. 1;

FIG. 4 a further embodiment of a manufacturing device according to theinvention comparable to FIGS. 1 and 3; and

FIG. 5 a perspective cutout view of a closure or adhesion product, whichcan be manufactured using a device according to FIG. 1 to 4 as well asthe method described below.

The manufacturing device according to FIG. 1 shows the basicconstruction in a horizontal manufacturing orientation. A band-shapedmolding screen 12, which is a component of a molding tool designated asa whole as 14, extends between two roller-shaped guide elements 10, ofwhich at least one can be driven. The molding screen 12 has a pluralityof individual molding cavities 16, which extend entirely through themolding screen 12, and the respective cavity 16 has the form of ahyperboloid of revolution when viewed from the side according to theenlarged longitudinal section X according to FIG. 1, reproduced in FIG.2. Other cavity shapes are also possible here however, depending on thepredeterminable shape of the final product that is to be produced.

Viewed in the direction shown in FIG. 1, an additional band 18 extendswithin the band-shaped molding screen 12, which additional band formsclosed surfaces and in this respect, is not provided with cavities, atleast in those regions in which the band 18 covers the cavities 16 ofthe band-shaped molding screen 12. The side 20 of the additional band 18facing the molding screen 12 thus forms a counter-face, which togetherwith the boundary walls 22 (pg. FIG. 3) of the individual moldingcavities 16, delimits the respective shaping zone of the molding screen12.

The bands 12 and 18, which are divided in the manner of an upper run andlower run, have a predeterminable width (not shown) extending into theplane of the drawing, and the cavities 16, only shown in a single planein FIG. 1, likewise extend in the plane of the drawing over apredeterminable distance. The screening band 12 thus formed may haveseveral hundred, thousand, or ten thousand or more through holes in eachcm² band material surface. To ensure better understanding however, thepertinent proportions are not taken into account in the depiction inFIG. 1.

The drive direction of the guide elements 10 is shown by means of arrowsin FIG. 1, so that in the selected drive direction, the two bands 12 and18 move from left to right as viewed in FIG. 1 with reference to theupper run layer of both bands 12, 18, and with both bands having thesame axial movement speed. The two bands 12 and 18 are separatecomponents however, and are separated from one another with theexception of the common attachment with one another, so that the abovementioned counter-face 20 of the additional band 18, together with thecontact surface 24 of the molding screen 12 facing the additional band18, encloses ambient air, wherein, although the ambient air thusenclosed can enter the individual cavities 16, the predeterminablequantity of air, which is located in the respective shaping zone, issubjected to a counter-pressure by means of a seal in the region of thescreen parts 25 of the molding screen 12, so that the air enclosed inthe cavity 16 cannot readily be displaced outward into the environmentduring the shaping process.

Insofar as the manufacturing device according to FIG. 1 is operatedwithin the context of a closed system (not shown), in principle it isalso possible to operate the manufacturing device within a mediumchamber, in which nitrogen may be introduced, for example, instead ofambient air. In principle, other working gases such as argon, helium,etc. may also be used here, so that a surface modification for theclosure or adhesion product that is to be produced by means of thedevice may be performed with such noble gases if necessary.

In addition, the device according to FIG. 1 has an application device26, for example in the manner of a conventionally formed extrudernozzle, which, having separate nozzles (not shown) on the undersidethereof, performs the extrusion application of an extrudable plasticmaterial into the molding cavities 16. The penetration of the plasticmaterial into the molding cavities 16 of the molding screen 12 may besupported by means of compression rollers 28, which are disposed on theopposite side of the bands 12, 18, wherein such an arrangement is onlyshown as an example in order to illustrate the function of said rollers.In reality, both the application device 26 and the respectivecompression roller 28, which also performs a supporting and guidingfunction, have a substantially more complicated design that what isshown in this case.

As shown in the enlarged section of the image detail X according to FIG.2, the plastic material is extruded in the manner of a dome 32 (shown asa broken line) into the associated molding cavity 16 by the design ofthe band-shaped support 30, wherein the remaining quantity of air 34 inthe shaping zone is increasingly reduced, so that a counter-pressure isexerted on the front side of the dome 32. This counter-pressuretherefore builds up because the enclosed quantity of air cannot bedisplaced into the environment 34 due to the seal established betweenthe contact surface 24 of the screening band 12 and the facing side orcounter-face 20 of the additional 18. In addition to a stem part 36,further entry of the plastic material into the molding cavity 16 alsocreates a widened head part 38 (see also FIG. 4) at the end of said stempart, wherein the quantity of air 34 that is not displaced can introducea concave indentation 40 at the free front end of the head part 38(shown as a dashed line in FIG. 3). The process of air displacement canalso be controlled such that a flat upper side of the head without aconcave indentation may also be created by completely displacing thequantity of air 34. The manufacturing process addressed proceedscontinuously, in which plastic material is continuously filled into theinitially empty cavities 16, which are moving to the right, by means ofthe extrusion device 26.

As FIG. 2 additionally shows, when viewed in cross-section, the sideflank end 42 of the head part 38 tapers outward to the surroundings, sothat the edge 42 at the flank end of the head part 38 is formed suchthat it is correspondingly flexible and pliable; nevertheless, itexhibits the rigidity needed for hooking or adhesion. Also contributingto this is the fact that the quantity of air displaced by thecounter-pressure results in a reinforced orientation alignment in theregion of the flank end 42 of the head part 38, in which the displacedair provides the plastic material in the region of the respective stempart 36 with a longitudinal orientation when viewed in the axialdirection, and the respective head part 38 with a uniform transverseorientation when viewed in a longitudinal direction, by means of thedirection of flow on all sides thereof. The above mentionedmacromolecular orientation of the plastic material as a result of thecounter-pressure allows the closure or adhesion product 44, includingthe support side 30 thereof, to be formed thin enough that the endproduct 44 according to the depiction in FIG. 4 is not only softer andmore flexible than previous comparable products, but also, in terms ofthe possible reduction of the free material cross-sections, allows amore rapid cooling of the plastic material within the molding screen 12,so that the plastic material in the respective cavity 16 hardens morequickly, with the result that molding can be done more quickly than inprevious process solution, resulting in faster operation of the moldingtool 14 as a whole.

The above mentioned bands 12 and 18 are preferably formed out of metalmaterials, however other material combinations are also possible; inparticular the additional band 18 could also be made out of a plasticmaterial having an especially good sealing action. The band 18 may alsohave a coating that improves the sealing effect, or may be formed as amulti-layered structure, for example in the form of a well-sealed firstlayer and stabilizing second layer, which is formed out of a differentmaterial than that of the first layer. As FIG. 1 further shows, thefinished closure or adhesion product 44 can then be removed from themolding device for later application by means of a discharge roller 46.A heating and/or cooling device 48 may also be disposed in the region ofsuch a shaping zone, with which the curing process may be optimized.

In order to achieve an especially good sealing effect in the regionwhere the counter-face 20 of the cover band 18 comes into contact withthe contact surface 24 of the molding screen 12, at least one of the twosurfaces is provided with a roughness Rz of 0.02 to 2.5 μm, preferablyin the range of 1.3 μm.

The method according to the invention for producing a closure oradhesion product according to the depiction in FIG. 4 may, in principle,be achieved by means of a thermoplastic, wherein polypropylene,polyamide or polyethylene are preferably used, depending on the intendeduse. Copolymers, or terpolymers, respectively, containing one or more ofthe thermoplastic resins mentioned are suitable.

If the later use of the end product is intended in particular foradhesion processes with third components, polyvinyl siloxane inparticular, or any plastic having a corresponding thixotropic behaviormay be used as a plastic material, wherein in the case of these plasticmaterials, which should have a rotational viscosity, as measured using arotation viscometer, of between 7,000 to 15,000 mPas, preferably howevera value of approximately 10,000 mPas, with a shear rate of 10 1/S.

FIG. 3 shows a manufacturing device that is modified as compared to FIG.1, having a production direction that is essentially vertical. Insofaras the components used in FIG. 3 correspond to the components in FIG. 1,the same reference characters will also be used in FIG. 3. Explanationsthat have already been provided in this respect shall also apply to theembodiment of the manufacturing device according to FIG. 3.

An essential difference between the two manufacturing devices, however,is that both the band-shaped molding screen 12 and the additional band18 are now disposed in turn in a closed manner as a molding tool 14 on acylindrical molding drum 50. In turn, the plastic material is introducedinto the cavities 16 of the molding device by means of the extruder-likeapplication device 26 in order to form the end product 44. In thepresent embodiment of the manufacturing device, however, instead of theabove-described compression rollers 28, an intrinsically closed pressingand contact band 54 is guided by means of deflection rollers 52 in thedirection of the arrow, in order to ensure the continuous introductionand retention of the plastic material in the respective molding cavity16. The band 54, which is formed as a single piece, thus forms a kind ofcounter surface opposing the additional band 18 in this regard, sealsthe cavities 16 against the environment in the other direction, likewisein a sealing manner, wherein in particular the band-shaped support part30 made of a plastic material improves the seal against the outside inthe manner of an additional sealant. Furthermore, when viewed in termsof the width, the contact band 54 in turn extends into the plane of thedrawing of FIG. 3 across the entire width of the drum-like molding tool14, at least far enough that, insofar as cavities 16 are present, thesecavities are also completely covered by the contact band 54.

FIG. 4 shows a manufacturing device that has been modified as comparedto those in the previously presented manufacturing devices in that thecavities 16 of the molding screen 12 are disposed directly on thecylindrical guide element 10. The rotational direction of the guideelement 10 is indicated by an arrow in FIG. 4. By means of the extruderor application device 26, in turn, the plastic material is nowintroduced into the cavities 16 of the molding screen 12 by means of ablade device 55. The necessary seal between the molding screen 12 andthe guide element 10 is thus implemented by the outside of the mold 10and the inside of the molding screen 12 in the region where the plasticis applied by means of the blade device 55.

In a further embodiment of a manufacturing device not shown here, thescreen 12 may also be entirely around the cylindrical guide elements, sothat in a concentric structure, the cylindrical molding screen 12encloses the cylindrical guide elements 10 while maintaining thenecessary fit size to form a seal.

FIG. 5 on the other hand, shows the completed end product, which may beproduced using the manufacturing devices according to the FIGS. 1 to 4.The end product is characterized in that the height thereof, between theunderside of the support 30 and the upper side of the support 30, is lowenough, preferably equaling 40 to 120 μm, particularly preferably 70 to110 μm, that the product has elastic properties at least in partialregions, especially in the longitudinal direction of the support 30.

If a conventional thermoplastic such as polypropylene, polyamide,polyethylene, etc. is used, the flank ends 42 of the respective headpart 38 will be formed sufficiently rigid, due to the above describedorientation of the plastic material due to the enclosure of air in therespective cavity 16, so that the underside of the respective flank end42 provides a secure hooking ability for the lower grip of a loop typematerial for an additional hook and loop component not shown here, inorder to form the Kletten® hook and loop fastener. Closure parts, suchas those depicted in FIG. 4, may also interact with the same closureparts (not shown) of a further hook and loop fastener in order tolikewise form such a fastener that can be repeatedly opened or closed,which fastener then has mushroom-shaped head parts 38 on both sides ashooking means.

The stem parts 36 shown in FIG. 5 as well as the head parts 38 are eachformed having a polygonal shape, in particular a hexagonal shape.Cylindrical stem parts (not shown), or stem parts having other shapes,may also be achieved depending on the shape geometry of the respectivemolding screen 12.

If polyvinyl siloxane or another plastic material having the specifiedthixotropy is preferably used, however, an adhesive product will beformed from a closure, in which the free end faces of the head parts 38may adhere to other surfaces, in particular of third components, underthe action of the van der Waals forces. The method according to theinvention as well as the manufacturing devices thereof thus may beadapted in such a way that on one occasion the described closure productmay be obtained, and on another occasion, the specified adhesionproduct.

1. A method for producing a plastic product consisting of a support (30)having protruding stem parts (36), which have at their free end a headpart (38) having a wider diameter as compared to the respective stempart (36), wherein the stem parts (36) and the head parts (38) areformed in cavities (16) of a molding screen (12), which cavities areformed on the side thereof facing away from the support (30) in ashaping zone of the molding screen (12), characterized in that theshaping zone is sealed off from the environment by means of acounter-face (20) in such a way that a predeterminable quantity of airenclosed in the shaping zone exerts a counter-pressure on the plasticmaterial introduced into the respective cavity (16) in order to supportthe shaping process.
 2. The method according to claim 1, characterizedin that the sealing of the shaping zone is achieved by means of thesurface configuration of the facing surfaces of the molding screen (12)and/or counter-face (20).
 3. The method according to claim 2,characterized in that at least one of the two surfaces is provided witha roughness Rz of 0.02 μm to 2.5 μm, preferably of 1.3 μm.
 4. The methodaccording to claim 1, characterized in that the shaping zone formed bythe respective cavities (16) has screen parts (25) in the molding screen(12), which can be brought in contact with one another with thecounter-face (20) of the band (18) during the shaping process in orderto form a seal.
 5. The method according to claim 1, characterized inthat the counter-face (20) and the molding screen (12) consists ofroller-like and/or of bad-shaped device components (12; 18) of which atleast one device component (12; 18) is driven for continuouscirculation.
 6. The method according to claim 1, characterized in thatthe respective cavity (16) within the molding screen (12) is formed inthe manner of a hyperboloid of revolution.
 7. The method according toclaim 1, characterized in that a thermoplastic or plastic having high athixotropic value is used as a plastic material.
 8. A device forcarrying out the method according to claim 1, characterized in that ashaping zone of a molding screen (12) can be sealed against theenvironment by means of a counter-face (20) such that a predeterminablequantity of air enclosed in the shaping zone exerts a counter-pressureon the plastic material introduced into a respective cavity (16) of theshaping zone in order to support the shaping process.
 9. The deviceaccording to claim 8, characterized in that the sealing of the shapingzone is achieved by means of the surface configuration of the facingsurfaces of the molding screen (12) and/or counter-face (20).
 10. Thedevice according to claim 9, characterized in that at least one of thetwo surfaces is provided with a roughness Rz of 0.02 to 1 μm, preferablyof 0.1 μm.
 11. A closure or adhesion product, produced according to amethod as well as a device according to claim 1, characterized in thatthe height of the product (44) between the underside of the support (30)and the upper side of the same support (30) is low enough, preferablyequaling 40 to 120 μM, particularly preferably 70 to 110 μm, that theproduct (44) has elastic properties at least in partial regions,especially in the longitudinal direction of the support (30).